Most people think about a drain port, and they create a low point tee piece to let the water out but they forget that air needs to get in to replace the water coming out! It can be difficult to get the water out of a closed loop, even with drains. My advice is be prepared to cut out and replace all your tubing, which isn't a bad idea to replace once a year or two.
Which leads to me to ask, why did you put a cleaning solution through a newly built loop? That makes no sense, you should be cleaning each component prior to installation.